1. Field of the Invention
The present invention relates to a pattern antenna formed on a circuit board. The present invention relates particularly to a pattern antenna that is compact and lightweight but that nevertheless permits wide-range transmission and reception, and to a wireless communication device equipped with such a pattern antenna.
2. Description of the Prior Art
In mobile communication using compact wireless devices such as cellular phones or indoor wireless LAN (local area network) terminals, those wireless devices, used as mobile units, need to be equipped with compact, high-performance antennas. As compact antennas for such applications, slim planar antennas have been receiving much attention because they can be incorporated in devices. As planar antennas are used microstrip antennas, of which typical examples are short-circuiting microstrip antennas as shown in FIG. 20A and planar inverted-F-shaped antennas as shown in FIG. 20B. In recent years, as wireless devices are made increasingly compact, planar antennas obtained by farther miniaturizing microstrip antennas as shown in FIG. 20A have been proposed, for example, in Japanese Patent Applications Laid-Open Nos. H5-347511 and 2000-59132.
The antennas proposed in Japanese Patent Applications Laid-Open Nos. H5-347511 and 2000-59132 are miniaturized as compared with common planar or linear antennas that have conventionally been used. However, either of these antennas is formed three-dimensionally on a circuit board, and thus requires a space dedicated thereto on the circuit board to which it is grounded. This sets a limit to the miniaturization of these types of antenna.
FIG. 22 shows the frequency response of the voltage standing wave ratio (VSWR) of an inverted-F-shaped printed pattern antenna 100 as shown in FIG. 21. In FIG. 21, the inverted-F-shaped printed pattern antenna 100 consists of an elongate pattern 100a that is formed parallel to a side edge of the grounding conductor portion 101 that faces it, a grounding conductor pattern 100c that is connected at one end to the end of the elongate pattern 100a opposite to the open end 100d thereof and that is connected at the other end to the grounding conductor pattern 101, and a feeding conductor pattern 100b that is connected at one end to a point on the elongate pattern 100a between the open end 100d of the elongate pattern 100a and the grounding conductor pattern 100c and that is connected at the other end to a feeding transmission path 102. As FIG. 22 shows, the inverted-F-shaped printed pattern antenna 100 configured in this way is usable only in a narrow frequency range.
On the other hand, Japanese Patent Application Laid-Open No. H6-334421 proposes a wireless communication product that employs a circuit-board-mounted antenna such as an inverted-L-shaped printed pattern antenna. However, on its own, an inverted-L-shaped printed pattern antenna is usable only in a narrow frequency range as described above. According to another proposal, an inverted-L-shaped printed pattern antenna is used together with a microstrip-type planar antenna to make it usable in a wider frequency range. However, this requires an unduly large area to be secured for the antennas, and thus hinders their miniaturization.
An object of the present invention is to provide a pattern antenna that is miniaturized by the use of a pattern antenna that is formed as a pattern on the surface or inside a circuit board, and to provide a wireless communication device equipped with such a pattern antenna.
To achieve the above object, according to one aspect of the present invention, a pattern antenna formed on a circuit board is provided with an inverted-F-shaped antenna pattern that is formed on a surface of the circuit board, has one end serving as a feeding portion and the other end left as an open end, has a bent portion formed between the feeding portion and the open end, with the portion of the inverted-F-shaped antenna pattern between the feeding portion and the bent portion serving as a feeding conductor pattern, and has a grounding conductor pattern formed so as to extend from a point between the feeding portion and the open end. Here, at least one of the feeding conductor pattern and the grounding conductor pattern is formed so as to have a trapezoid shape.
According to another aspect of the present invention, a pattern antenna formed on a circuit board is provided with an inverted-L-shaped antenna pattern that is formed on a surface of the circuit board, has one end serving as a feeding portion and the other end left as an open end, and has a bent portion formed between the feeding portion and the open end, with the portion of the inverted-L-shaped antenna pattern between the feeding portion and the bent portion serving as a feeding conductor pattern. Here, the feeding conductor pattern is formed so as to have a trapezoid shape.
According to another aspect of the present invention, in a wireless communication device having a pattern antenna that permits at least either transmission or reception of a communication signal to or from an external device, the pattern antenna is provided with an inverted-F-shaped antenna pattern that is formed on a surface of the circuit board, has one end serving as a feeding portion and the other end left as an open end, has a bent portion formed between the feeding portion and the open end, with the portion of the inverted-F-shaped antenna pattern between the feeding portion and the bent portion serving as a feeding conductor pattern, and has a grounding conductor pattern formed so as to extend from a point between the feeding portion and the open end. Here, at least one of the feeding conductor pattern and the grounding conductor pattern is formed so as to have a trapezoid shape.
According to another aspect of the present invention, in a wireless communication device having a pattern antenna that permits at least either transmission or reception of a communication signal to or from an external device, the pattern antenna is provided with an inverted-L-shaped antenna pattern that is formed on a surface of the circuit board, has one end serving as a feeding portion and the other end left as an open end, and has a bent portion formed between the feeding portion and the open end, with the portion of the inverted-L-shaped antenna pattern between the feeding portion and the bent portion serving as a feeding conductor pattern. Here, the feeding conductor pattern is formed so as to have a trapezoid shape.